ContentProvider具有多个表 [英] ContentProvider with multiple tables

问题描述

我想实现一个操作多个表的 ContentProvider 。这是我到目前为止所尝试的。我写了一个Java 接口，表示每个表应该在其CRUD类中实现的CRUD操作。

I want to implement a ContentProvider that manipulates multiple tables. Here is what I tried so far. I wrote a Java Interface that represents the CRUD operations that every table should implement in its CRUD class.

public interface CRUDHandler {
    //UPDATE
    int update(Uri uri, ContentValues values, String selection,String[] selectionArgs);
    //READ
    Cursor query(Uri uri, String[] projection, String selection,String[] selectionArgs, String sortOrder) ;
    //CREATE
    Uri insert(Uri uri, ContentValues values);
    //DELETE
    int delete(Uri uri, String selection, String[] selectionArgs);
    //get Mime type
    String getType(Uri uri);
}

然后我写了一个抽象 class 定义了 ContentProvider 的静态 UriMatcher 所以每个类扩展这个类应该添加它的 Uri 来标识它，并为接口中的每个方法提供一个实现。

Then I wrote an abstract class that defines a static UriMatcher for the ContentProvider so each class that extends this class should add its Uri that identifies it and provide an implementation for each method in interface.

类看起来像这样：

public abstract class  ApplicationCRUD  implements CRUDHandler{

    public static final UriMatcher sUriMatcher;

    static {
        sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
    }
}

此外，我为每个表创建了一个类， code> extends 这个类，并将 Uri 添加到 UriMatcher 来自抽象类。

Further, I created a class for each table that extends this class and adds its Uri's to the UriMatcher from the abstract class.

这是一个例子：

public class Table1CRUD extends ApplicationCRUD {
    //Setup Projection Map for Table1 
        private static HashMap<String , String>sTable1ProjectionMap;
        static {
            sTable1ProjectionMap.put(ApplicationProviderMetaData.Table1MetaData._ID, ApplicationProviderMetaData.Table1MetaData.TABLE_NAME+"."+ApplicationProviderMetaData.Table1MetaData._ID);
            sTable1ProjectionMap.put(ApplicationProviderMetaData.Table1MetaData.COL1, ApplicationProviderMetaData.Table1MetaData.TABLE_NAME+"."+ApplicationProviderMetaData.Table1MetaData.COL1);
            sTable1ProjectionMap.put(ApplicationProviderMetaData.Table1MetaData.COL2, ApplicationProviderMetaData.Table1MetaData.TABLE_NAME+"."+ApplicationProviderMetaData.Table1MetaData.COL2);
        }

        public static final int INCOMING_SINGLE_URI_INDICATOR = 5;
        public static final int INCOMING_COLLECTION_URI_INIDICATOR = 6;
    static {
        //standard URI 
        sUriMatcher.addURI(ApplicationProviderMetaData.AUTHORITY, "t1", INCOMING_COLLECTION_URI_INIDICATOR);
        sUriMatcher.addURI(ApplicationProviderMetaData.AUTHORITY, "t1/#", INCOMING_SINGLE_URI_INDICATOR);
        //here add your custom URI 

    }
    @Override
    public int update(Uri uri, ContentValues values, String selection,
            String[] selectionArgs) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public String getType(Uri uri) {
        // TODO Auto-generated method stub
        return null;
    }

}

现在我的 ContentProvider 看起来像这样：

Now my ContentProvider looks like this:

public class ApplicationProvider  extends ContentProvider{
    //Define TAG FOR EACH CLASS FOR DEBUGGING 
    private static final String TAG = "ApplicationProvider";
    // Application CRUD Handlers use to support multiple tables inside the content provider
    private static Table1CRUD table1CRUD;
    private static Table2CRUD table2CRUD;

    static {
        table1CRUD = new Table1CRUD();
        table2CRUD= new Table2CRUD();

    }
    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        int uriMatchResult = ApplicationCRUD.sUriMatcher.match(uri);
        //case Table1
        if(uriMatchResult == Table1CRUD.INCOMING_COLLECTION_URI_INIDICATOR ||uriMatchResult == Table1CRUD.INCOMING_SINGLE_URI_INDICATOR )
        {
            return table1CRUD.delete(uri, selection, selectionArgs);
        }
        case Table2
        else if(uriMatchResult == Table2.INCOMING_COLLECTION_URI_INDICATOR|| uriMatchResult ==Table2.INCOMING_SINGLE_URI_INDICATOR){
            return table2CRUD.delete(uri, selection, selectionArgs);
        }

        else{
            throw new IllegalArgumentException("Unknown Uri "+uri);
        }
    }

现在我使用 SQLiteOpenHelper 作为 ContentProvider
中的私有类，我在我的 ContentProvider 。应该修改接口并提供对象依赖注入的每个CRUD方法，让每个函数使用它来访问数据库？我也想知道你对这种方法的看法：是否够好？这是否使我想要有效地做的事情？

Now I am using the SQLiteOpenHelper as a private class in the ContentProvider and I define an instance of it in my ContentProvider. Should I modify the interface and supply each CRUD method that object Dependency Injection to let each function use it to access the database? I also want to know what you think about this approach: Is it good enough? Does it make the thing I am trying to do efficiently? What modification can I do to improve this design?

推荐答案

Google IO Schedule 应用程序是一个很好的资源，如果你需要设计一个具有多个表的 ContentProvider 。听起来你想做一些更复杂的事情，但也许会有所帮助。

The Google IO Schedule application is a good resource if you are need to design a ContentProvider with multiple tables. It sounds like you want to do something a bit more complicated, but maybe it will help.

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